4305 Elements are specially designed to be used with the 4035 Wattmeter and are calibrated in accordance with meticulous Bird calibration procedures supported by a long history of mean deviation values to assure adherence to advertised specifications of current instruments, as well as field interchangeability with equipment purchased, used and trusted in all the years since its introduction. Listed accuracies can, of course, not be guaranteed with components not supplied by Bird.
